In the semiconductor industry, lithography systems are used to create, i.e. fabricate electronic devices, typically in the form of integrated circuits formed on silicon wafer, commonly referred to as semiconductor chips. Photolithography utilizes reusable optical masks to project an image of a pattern representing the desired circuit structures onto a silicon wafer as part of the manufacturing process. The mask is used repeatedly to image the same circuit structures on different parts of a silicon wafer and on subsequent wafers, resulting in a series of identical chips being fabricated from each wafer, each chip having an identical circuit design.
Various technologies relating to security, such as data security, secure communications, traceability, authentication, anti-counterfeiting etc., create an increasing need for unique chips having unique circuits or codes, or other unique hardware features for diversification of the chips. Such unique chips are known and often implement a security related operation in an obfuscated manner requiring the chip to be truly unique. The known unique chips are typically realized after the manufacture of a chip, e.g. by manufacturing a series of identical chips using conventional mask-based photolithography and then, after manufacture, disrupting certain connections in the chip or by assessing the uniqueness of the chip afterwards upon inspection and control of certain features. The masks used in this process are expensive to produce, and manufacturing unique masks for each single chip is clearly much too expensive, for which reason mask based photolithography is considered unsuitable for fabricating unique chips.
Semiconductor chips can be created to contain predetermined data or code, i.e. in the form of readable data, typically using mask ROM (MROM), erasable programmable read-only memory (EPROM) or electrically erasable programmable read-only memory (EEPROM). The MROM variant uses masked-based lithography to create the ROM including the data stored permanently in the ROM, with the above identified drawbacks of mask-based lithography when creating chips with unique codes. EPROM and EEPROM allow the data to be written to the ROM at a later stage, but this disadvantageously takes control over the code away from the manufacturing process and introduces security risks.
It has been suggested to utilize maskless lithography for the purpose of creating unique chips. With maskless lithography no hard mask is used, and instead the required pattern representing the circuit design is input to the maskless lithography system in the form of a design layout data file such as a GDSII or OASIS file containing the circuit design layout to be transferred to the target, e.g. wafer, to be exposed by the maskless lithography system.
A maskless lithography and data input system is disclosed in WO 2010/134026 in the name of Applicant of the present invention. WO 2010/134026 is hereby incorporated by reference in its entirety. The disclosed maskless system writes patterns onto wafers directly using charged particle beamlets such as electron beamlets. Because the desired pattern for exposing each chip is represented as data instead of a mask, it becomes possible to utilize such system for the manufacture of unique chips. The pattern data that is input to the exposure system, representing the unique electronic devices or chips to be created, may be made unique by using a different design layout data input file, e.g. a GDSII or OASIS input file, for each unique electronic device to be created.
WO 2011/117253 and WO 2011/051301, both assigned to the Applicant of the present invention and hereby incorporated by reference in their entirety, disclose various examples of electronic devices or chips that can be created using a charged particle lithography system.